Three Chinese engineers were killed and eleven others injured in a car bomb attack by suspected militants in southwest Pakistan on Monday, police sources said.

The attack took place at around 0940 IST as 12 Chinese engineers were being transported by a coach to Gwadar port, about 500 kilometers west of Karachi, near the border with Iran, Sattar Lasi, the chief of police in Gwadar said.

"A car was parked near the port and it exploded as the bus reached the port," he said, adding it was not clear if it were a suicide attack.

A Pakistani driver and gunman were also injured in the attack, Lasi said.

The Chinese engineers were working on a seaport project in Gwadar.

Masood Baloch, a doctor in Gwadar hospital, confirmed the death of three people. He said four of the injured were in critical condition and have been shifted to Karachi by a plane. He said all the injured except two are foreigners.

This is perhaps the first time in Pakistan that Chinese were targeted. China is Pakistan's most important ally and its chief trading partner.

The attack resembled a car bomb attack on May 8, 2002 in which Pakistani militants attacked a bus carrying French engineers outside the Sheraton hotel in Karachi, killing 11 of them. The French had been helping the Pakistani armed forced develop a submarine.